Electrochemical battery with mobile electrodes

ABSTRACT

An electrochemical battery with mobile electrodes of the so-called &#34;reserve&#34; type. According to one characteristic of the invention, the battery includes a holder for holding the electrodes outside the cells during a storage period of the battery, and for placing these electrodes inside the cells in order to activate the battery.

BACKGROUND OF THE INVENTION

This application is a 371 of PCT/FR92/00826 filed Aug. 28, 1992.

1. Field of the Invention

The invention relates to electrochemical batteries, especiallyelectrochemical batteries of the so-called "reserve" type. Itparticularly relates to means for producing the activation of suchbatteries.

2. Description of the Related Art

Electrochemical batteries of the reserve type are batteries intended tobe set in operation after a storage period whose duration is variableand may extend for example up to 15 years and more.

This type of battery is widely used in order to provide electricalenergy in ballistic devices, for example shells, missiles, etc. However,these batteries are also of great interest in other fields, for examplethat of security devices.

Batteries of the reserve type provide electrical energy from the instantwhen they are activated. The activation of the battery consists inuniting the different elements which, conventionally, convert thechemical reaction into electrical energy.

Such an electrochemical battery may comprise one or more electrochemicalcells, the number of these cells being a function of the voltage to beobtained. In operation, that is to say after activation, each cellcomprises two electrodes of opposite polarities in contact with aquantity of liquid electrolyte.

Most often, the liquid electrolyte is held outside the cell in a storagereservoir until the instant of activation. The activation of the batteryconsists in releasing the electrolyte.

In the case for example of rockets or artillery shells, during thestorage period, all the quantities of electrolyte necessary for all thecells are most often contained in a single storage reservoir. Theactivation of the battery consists in releasing the liquid electrolytefrom the reservoir and in bringing it into the cell or different cells.This activation may be obtained by combining the effects of the strongacceleration and of the speed of rotation which appear at the start ofthe shot: the electrolyte is released for example by breaking a capunder the effect of the longitudinal acceleration, at the instant offiring; and the electrolyte is distributed in the cells, aided to thiseffect by the centrifugal force due to the rotation of the device onitself.

In structures having a single storage reservoir for several cells, asignificant problem resides in the balancing, that is to say the mosteven distribution possible of the electrolyte between the various cells,while minimising communication between the cells. In fact, in the mostcommon case when the electrodes are of the "bipolar electrode" type, anyquantity of electrolyte contained in communication ducts between cellsgenerates a self-consumption phenomenon of the battery, which decreasesthe capacity of the latter for supplying energy to the working load.Furthermore, the electrolyte contained in these ducts may generate atroublesome fluctuation of the voltages delivered by the battery.

This leads in practice to the adoption of various compromises in theproduction of these batteries, which make the structure more complex,without thereby completely eliminating the problem of self-consumption.Examples of production of such reserve electrochemical batteries which"can be activated on firing" are found in particular in U.S. No. Pat.2,996,564 and in French Patent Applications No. 8,815,331 and 8,909,637.

It should be noted that the problem posed by the activation of thereserve batteries, in the case of rotating ammunition, is made stillmore difficult in the case when the battery is mounted in a missile orprojectile, which can undergo low accelerations, for example a mortarshell. The case of the mortar shell is actually particularly difficult,because of its low possible acceleration on starting, and the absence ofrotation.

Thus, the principles explained above for producing the release anddistribution of the electrolyte in the cells are inapplicable. Othersolutions are envisaged, which are technologically much more complex.

In fact, these more complex solutions do not yet appear to have beenachieved industrially. Hitherto, the electrical supply in mortar rocketshas been effected using turbine and alternator systems whoseimplementation is complex and expensive but which have the advantage ofbeing in existence.

The present invention relates to electrochemical batteries, inparticular of the reserve type. It particularly relates to means forproducing the activation of such batteries, and is applicable equallywell in the case of high or low accelerations, with or withoutcentrifugal force. It makes it possible to bring about very rapidactivation while avoiding the defects of self-consumption and of poordistribution of the electrolyte. Furthermore, the invention is wellsuited to economical industrial production, so much so that it may beapplied in numerous domains other than those already cited, for examplethe electrical supply of security devices, such as extinguishers,beacons, etc.

SUMMARY OF THE INVENTION

According to the invention, an electrochemical battery comprising atleast one cell, the cell comprising two electrodes of oppositepolarities and an electrolytic space containing an electrolyte, ischaracterised in that it furthermore comprises means for, on the onehand, holding the electrodes outside the cell during a period of storageof the battery, and, on the other hand, for placing these electrodes inthe cell in order to activate the battery.

This solution is particularly advantageous in that it allows theelectrolyte to be stored in the cell itself, in the position of use,such that the act of putting the electrode in place causes the immediateoperation of the battery. Furthermore, in the case of several cells, thedistribution of the electrolyte in the cells is always correct, becauseit is carried out during the manufacture of the battery.

DESCRIPTION OF THE DRAWINGS

The invention will be better understood, and other advantages andcharacteristics which it exhibits will emerge better on reading thedescription which follows, made with reference to the attached drawings,in which:

FIG. 1 shows a battery according to the invention through a sectionalview parallel to one cell;

FIG. 2 is a top view of the battery of the invention showing adistribution of several cells with their electrodes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 diagrammatically shows, by way of non-limiting example, anelectrochemical battery 1 according to the invention.

The battery 1 is of the reserve type. It comprises an enclosure 2,which, in the non-limiting example described, has a circular crosssection (represented by its diameter d1), the plane of this crosssection being perpendicular to that in FIG. 1. Several electrochemicalcells are arranged around a longitudinal axis 5 of the enclosure, ofwhich only two cells C2, C10 are represented in FIG. 1.

FIG. 2 is a top view of the battery 1, which view is symbolicallyrepresented in FIG. 1 by an arrow 4, and which shows the battery 1 incross section.

In the non-limiting example described, 14 consecutive electrochemicalcells C1 to C14 are distributed around the longitudinal axis 5 with apitch p; the longitudinal axis 5 being perpendicular to the plane ofFIG. 2, it appears on the latter as a point. Obviously, in the spirit ofthe invention, these cells may be arranged differently and there may bea different number of them, greater or smaller, it being possible forthere to be only a single cell.

Each cell C1 to C14 comprises two electrodes E, E+ of oppositepolarities located on either side of a space called the "electrolyticspace"7 containing an electrolyte 8.

The electrochemical cells C1 to C14 are mounted in series and add thevoltages which they produce, so that the total electromotive force isavailable between two outputs "+", "-" , one of which is the positivepolarity delivered by an electrode E+, of the first cell C1, and theother "-" is the negative polarity delivered by the electrode E- of thelast cell C14.

In a manner which is per se conventional, the electrodes E-, E+ consistof bipolar plates, that is to say that they are carried by separatingplates P1 to P15, on the two opposite large faces of the latter: theseparating plates P1 to P15 are made of a conducting material of whichone face is covered for example with lead in order to form a negativeelectrode E-, and the other face of which is covered for example withlead dioxide (PbO₂) in order to form a positive electrode E+.

Thus, for example, the third separating plate P3, which separates thesecond and the third electrochemical cells C2 and C3, carries on oneface the negative electrode E- of the second cell C2, and carries itsopposite face the electrode E+ of the third cell C3.

The separating plates P1 and P15 do not in principle need theirdeposition E- (for P1) and E+ (for P15), but for reasons of economy, itis simpler in practice to produce them in the same plate as the others,although the face forming E- in the case of P1 and the face forming E+in the case of P15 do not have any electrical role.

The electrolytic space 7 is delimited in each cell C1 to C14 between thetwo electrodes E+ , E- and between 3 insulating walls: the first calleda peripheral wall 10 is on the side of the enclosure 2; the secondsituated opposite the first is called the central wall 11, it consistsfor example of a ring of insulating material 13 centred on thelongitudinal axis 5; the third insulating wall being formed by theinsulating bottom 21 of the cell.

In each cell C1 to C14, the peripheral and central walls 10, 11 areseparated by a distance D1 called the separation distance which extendsparallel to radii (not represented) of the enclosure 2.

According to one characteristic of the invention, when the battery 1 isin operation, the separating plates P1 to P15 have a length L1 parallelto the separation distance D1 and greater than the latter, so that eachof the lateral edges 16, 17 of the separating plates P1 to P15 extendfurther and are driven into the peripheral and central insulating walls10, 11. These lateral edges 16, 17 are thus clamped in the walls 10, 11and protected from any contact with the electrolyte 8, in order to avoidthe phenomenon of self-consumption.

Again with reference to FIG. 1, the latter represents, in particular, onthe one hand, the second cell C2 in a left-hand portion of the figuresituated in a box labelled 25; and it represents in particular the tenthcell C10 in a second box labelled 26.

The box 25 has the purpose of illustrating the storage position of thebattery, that is to say its non-activated state, and therefore the onein which it does not function. The box 26 has the purpose ofillustrating the activated position, when the battery is set inoperation.

According to another characteristic of the invention, in the storageposition of the battery, the electrodes E+ , E- are retained outside thecells C1 to C14. This is illustrated by the box 25, in which theseparating plate P3 is retained separated from the electrolytic unit 30constituted by the various cells C1 to C14 which each contain anelectrolyte 8.

The third separating plate P3 carries on its visible face a negativeelectrode E- intended for the second cell C2, and carries on the otherface a positive electrode E+ intended for the third cell C3.

According to the invention, the activation of the battery 1 is obtainedby putting in place the various electrodes E+, E- in the various cellsC1 to C14. For this purpose, all the separating plates P1 to P15 aremoved from a top position (shown in the box 25) to a bottom position(shown in the box 26) where they are engaged between the various cellsC1 to C14 until they bear on the insulating bottom 21 of the cell, thatis to say the bottom with which the electrolyte 8 is in contact.

This latter position of the separating plates P1 to P15 is illustratedin the box 26 in which it is seen that a positive electrode E+, formingthe visible face of the tenth separating plate P10, is placed inside thetenth cell C10.

It can be seen, as previously indicated, that the separating plate P10has a length L1 greater than the separation distance D1, so that itslateral edges 16 and 17 are engaged in the insulating walls 10, 11.Furthermore, the separating plates have a height H1 which is greaterthan the depth H2 of the electrolytic space 7, so that when they are inplace, on the one hand they have a lower edge 18 which penetrates intothe insulating bottom 21, and on the other hand they have an upper edge19 (opposite the lower edge 18) which remains outside the electrolyticspace 7.

In the storage period, each cell C1 to C14 contains the quantity ofelectrolyte necessary for its operation, and the electrodes E+, E- areretained separated from the electrolytic unit.

The activation consists in placing the electrodes E+, E- in theelectrolytic unit, in contact with the electrolyte. This is achieved bya relative motion between the electrolytic unit and the separatingplates P1 P15, and as described above, the dimensions of the latter aresuch that, as they are driven into a cell, they penetrate the peripheraland central walls 10, 11 in which their lateral edges 16, 17 areembedded and isolated from the electrolyte, in the same way as theirlower edge 18 is driven into the bottom 21; this arrangement makes itpossible to avoid the phenomenon of self-consumption which occurs whenthe segment of a bipolar plate is bathed in the electrolyte.

Of course, the electrically insulating material from which the walls 10,11 and the bottom 21 are made must have a structure adapted to allow itto be penetrated by the edges of the plates without disintegrating, andto maintain a seal around these edges. Materials having the requisitequalities are for example elastomers, or gels of the silicone type.

The electrolyte may be in liquid form or alternatively and preferably insolid form, that is to say in the form of a gel.

Such a solid electrolyte, henceforth in the description termed an"electrolytic gel", may be obtained in a manner which is per se simple,by adding to the electrolyte gelling agents for example based oncolloidal silica or the like.

In the non-limiting example described where the electrodes E+, E- aremade of lead and of lead oxide, the electrolytic gel may for example bebased on colloidal silica, together with fluoroboric acid and diethyleneglycol.

Whatever the nature of the electrolyte 7, it is contained in the cellsC1 to C14 for the storage period, in the position and in the form of itsuse, that is to say that it is immediately usable with perfectdistribution in the cells. There is therefore no problem of balancingthe quantities of electrolyte between cells, as in the prior art,because the driving in of the separating plates P1 to P15 only has theeffect of separating the respective electrolyte parts of two consecutivecells C1 to C14 from each other. In fact, the insulating walls 10, 11and the bottom 21 as well as the electrolyte 8 may extend continuously:the cells C1 to C14 are actually created by the driving in of theseparating plates P1 to P15 or bipolar plates, which driving in has theconsequence of delimiting the electrolyte part allocated to each cell,and of placing the electrodes E-, E+ on either side of this electrolytepart. Of course, it is suitable for this purpose that, when they arebeing driven into the cells C1 to C14, the separating plates P1 to P15are held at defined positions around the longitudinal axis 5, withpredetermined separations between them which correspond to the pitch pof the cells C1 to C14.

For better preservation of the electrolytic gel, for example againstdrying-out, the zone containing the electrolyte, that is to say thesuccession of electrolytic spaces 7, may be covered with a leaktightfilm or cap 32, for example made of a heat-welded plastic. The cap 32furthermore produces mechanical holding of the electrolytic gel.

In the case of a liquid electrolyte, based on HBF₄ for example, the cap32 is necessary for keeping the electrolyte in its housing which isconstituted by the succession of electrolytic spaces 8.

Of course, the lid 32 is perforated by the lower edges 18 of theseparating plates P1 to P15, when the latter are driven into the cells.With a view to facilitating the penetration of the separating plates P1to P15 into the walls 10, 11, and the bottom 21, and possibly the cap32, the inner edge 18 and possibly the edges 16, 17 of these plates maybe made into cutting edges, for example by giving them a triangularshape (not represented).

The motion which is to lead to the electrodes E+, E- being driven intothe cells C1 to C14 may be obtained by moving the separating plates P1to P15 and/or by moving the electrolytic unit 30. For practical andmechanical reasons, it may be preferable to fix the latter in theenclosure 2, and to make the separating plates P1 to P15 mobile, as inthe non-limiting example represented in FIG. 1.

It is furthermore preferable to guide the plates P1 to P15, inparticular in the case of the example represented, where the cells C1 toC14 follow each other around a circle (see FIG. 2), and where the spacebetween the first and last cells C1, C14 is formed by an isolating space33 without electrolyte.

In the non-limiting example described, the separating plates P1 to P15are moulded onto a plastic article 38 which is common to all theseplates, so that all these plates are retained in the article 38 by theirupper edge 19.

The plastic article 38 extends above the succession of cells P1 to P3,and it carries the separating plates C1 to C15 with which it constitutesa possibly movable unit called the "electrode unit" 35. The separatingplates P1 to P15 are thus fixed to each other, and held with a spacingbetween them which corresponds to the pitch p with which the cells C1 toC14 are arranged.

The movement of the electrode unit 35 is symbolised by an arrow 29; itmust occur over a distance d2 which is that necessary to transport theseparating plates P1 to P15 from the storage position (represented inthe box 25) as far as the activated position where they are in thecells, as shown in the box 26.

In this movement, the electrode unit 35 may slide for example along aspindle 44 arranged along the longitudinal axis 5. The electrode unit 35may be guided in various ways, it may be guided for example with the aidof a rib 70 on the spindle 44.

The movement of the electrode unit 35 from the storage position as faras the activated position may be accomplished using various means whichare known per se, in particular as a function of the application of thebattery 1.

For example, if the battery 1 is used with an artillery shell which hasvery high acceleration, the electrode unit 35 may behave as an inertiablock whose inertia, at the instant of starting of the shell, causes themovement and consequently the driving in of the electrodes into thecells C1 to C14. It should, however, be noted that the force whichcauses the movement of the electrode unit 35 should be substituted forwhen it stops, in order to hold the separating plates P1 to P15 drivenin between the cells C1 to C14.

It is also possible to produce the movement of the electrode unit 35with the aid of a conventional activation device 40 using the pressureof a gas coming from a gas generator 41. The electrode unit 35 acts as apiston and slides on the central spindle 44 so as to be mobile along thelongitudinal axis 5, between two positions PS and PA: the first positionPS is that which is nearest an upper wall 38 of the enclosure 2, and itconstitutes the storage position, the second position PA being theactivated position. The electrode unit 35 is held at the storageposition PS by conventional means (not represented).

The generator 41 is, in the example, located in a space 43 formedbetween the electrode unit 35 and the upper wall of the enclosure 2.When it is time for the battery 1 to be activated, a gas released by thegenerator 41 pushes the electrode unit 35 like a piston, and causes theelectrodes E-, E+ to be driven into the cells C1 to C14. The gasgenerator 41 may be controlled conventionally, generally by anelectrical pulse.

With a view to holding the electrode unit 35 in the activation positionafter it is placed in position by the gas generator 41 (or by thestarting acceleration of the shot), the spindle 44 is equipped with anon-return device. Various means are known for this purpose. In thenon-limiting example described, this is accomplished with the aid of aspring plate 71, which, during storage, is retracted in the spindle 44itself; when the electrode unit 35 is driven in, the spring 71 escapesand thus prevents a return motion of the electrode unit 35.

With an appropriate sensor, an activating device 40 makes it possible toactivate the battery 1 in a large number of situations and applications:control by electrical pulse, percussion or other means.

It should be noted that an electrochemical battery according to theinvention is of very particular interest in the case of mortar rounds,because the placement of the electrolyte in the electrolyte cells andthe balancing of this electrolyte in the cells does not require thepresence of a centrifugal force.

In the non-limiting example in FIG. 2, the outputs "+" and "-" of theelectromotive force of the battery 1 (that is to say coming from thesetting of all the cells C1 to C14 in series) are symbolicallyrepresented as being available at first ends 60 of two connection wiresF1, F2; these outputs "+"and "-" being stationary. The two wires F1, F2are connected at their second ends 61 to the plates P1 and P15respectively, the electrical contacts being obtained for example bywelding.

If the electrodes are mobile, that is to say if the separating plates P1to P15 are driven in between the cells C1 to C14 as a result of amovement of these separating plates as previously explained, it isnecessary to connect the first and last plate P1, P15 to the stationaryconnections of the battery, for example by a flexible wire; the wiresF1, F2 then have a sufficient range of movement to take up the movementof the electrodes. Obviously, a spring-plate connection (notrepresented), which is per se conventional, may also be used, asdescribed for example in U.S. Pat. No. 4,331,848.

In the converse case, when the electrodes are stationary, the outputconnections are produced conventionally and simply on the electrodesthemselves.

We claim:
 1. An electrochemical battery having:a group of mobileelectrode carrying plates, said plates having electrodes affixedthereon; and a fixed electrolyte container having electrolyte therein,said electrolyte extending throughout said container in anuncompartmented manner when said battery is in a storage state wheresaid electrodes are out of contact with said electrolyte, and saidelectrolyte being compartmented into several individual portions, theindividual portions isolated from each other by said electrode carryingplates when said battery is in an activated state, the electrodes incontact with said electrolyte in the activated state.
 2. Anelectrochemical battery according to claim 1, wherein said electrodecarrying plates are translationally movable towards said container. 3.An electrochemical battery according to any of claims 1 or 2, whereinthe electrolyte is a gel.
 4. An electrochemical battery according to anyone of claims 1 or 2, wherein said electrode carrying plates eachcomprise two main faces, one of said faces carries an electrode of onegiven polarity and the other face carries an electrode of an oppositepolarity.
 5. An electrochemical battery having a storage state in whichthe battery is inactive and an activated state in which the battery isactive, said battery comprising several electrode carrying plates, eachplate having two main faces, one of said faces carries an electrode ofone given polarity and the other face carries an electrode of anopposite polarity, said battery further comprising an electrolytecontainer having electrolyte therein, means for maintaining theelectrode carrying plates out of contact with the electrolyte when saidbattery is in the storage state, means for allowing displacement of saidelectrode carrying plates towards and into said container during anactivation operation, and means for maintaining the plates in saidcontainer, when the battery is in the activated state, in a positionsuch that a respective pair of adjacent plates enclose a respectiveportion of said electrolyte, said portion isolated from other portionsby said pair of adjacent plates.
 6. An electrochemical battery accordingto claim 5, wherein said electrolyte is a gel.